Large-capacity pliable containers are used e.g. in the pharmaceutical industry or in the chemical industry.
They are intended to contain semi-finished products and finished products in solid form as powders, granules, tablets, or capsules, for example.
They are made of plastic material and have capacities from 100 to 600 liters.
They contain an inner protective envelope to be inserted into an outer envelope.
The packaging, consisting of one inner and one outer envelope, is disposable after use, which ensures that it is perfectly clean as it is used only once. This feature avoids risks of contamination unlike reusable rigid containers that need to be washed, aseptized, identified. The unit cost of use is much lower in the end and the risk of mixture of one batch with another is avoided.
The known outer envelopes consist of a woven polymeric material such as e.g. polypropylene, which is a strong material ensuring that the outer envelope is able to hold a load weighing from several dozen kilograms up to and even more than 500 kg.
The individual elements of the outer envelope are produced by cutting and are sewn together.
The inner protective envelope, commonly referred to as a bag or liner, must be perfectly tight. It is intended to protect the contents of the pliable container from its environment (moisture, smell, light, gas).
The inner protective envelope is made from a polymeric material, e.g. such as polyethylene. It can also be made from nobler materials, such as complex laminates based on aluminium, polyamide or technical plastics imparting more specific properties.
The materials used and the methods for producing inner protective envelopes must meet the highest standards of the pharmaceutical industry, in particular the requirements in terms of cleanliness, non-pollution and sterility.
The inner protective envelope is assembled with the outer envelope for producing the large-capacity pliable container.
Large-capacity pliable containers 2b of the prior art, as illustrated in FIG. 1, have a parallelepipedic shape with a square cross-section.
Pliable containers 2b are intended to be inserted into a metal frame 2a and supported thereby.
Due to their parallelepipedic shape of square cross-section pliable containers can only be used for metal frames having a square cross-section.
However, most storage racks used e.g. in the pharmaceutical industry are configured to accommodate containers of rectangular cross-section.
Inserting a pliable container of square cross-section into a metal frame of rectangular cross-section entails a loss in storage space.
Therefore, there is a need for pliable containers having a rectangular cross-section in order to increase the storage capacities and be able to use them within metal frames of rectangular cross-section, which are widely used in the industry.
Nevertheless, such pliable containers having a rectangular cross-section are not easily produced.
Actually, it is not possible to produce an inner protective envelope of rectangular cross-section using the manufacturing methods of the prior art.
Such inner protective envelopes of rectangular cross-section cannot be produced through the sole folding, cutting and soldering operations commonly used in this sector.
In particular, such operations are not likely to produce inner protective envelopes of rectangular cross-section having spouts of square cross-section.
Only square cross-sections can be obtained using the conventional folding methods.